1. Field
The presently disclosed subject matter relates to a vehicle lamp, and more particularly to a vehicle lamp such as a headlight, auxiliary headlight, indicator light, tail light, spot light, traffic light, or other vehicle lamp including a light source using a light-emitting semiconductor device.
2. Description of the Related Art
Recently, various vehicle lamps using an LED as a light source have been devised in accordance with an improvement of luminance efficiency of LEDs. For example, patent document No. 1 (Japanese Patent Application Laid Open JP2001-076513) and patent document No. 2 (Japanese Patent Application Laid Open JP2001-216814) disclose a basic structure of a conventional vehicle lamp using an LED as a light source as shown in FIG. 8.
The vehicle lamp 1 is composed of an LED 2 and an inner lens 3 located in front of the LED 2. The LED 2 is mounted on a circuit board 2a and an optical axis O thereof is perpendicular to the circuit board 2a. The LED 2 is emitted while being controlled by a driving circuit and virtually operates as a point light source. The inner lens 3 includes a lens formation 3a thereon that is configured to form a light distribution pattern so as to conform to a regulation such as a light distribution standard in accordance with traffic laws.
According to the vehicle lamp 1 of the above-described structure, the LED 2 is emitted and driven by a driving circuit. Light emitted from the LED 2 travels forward along the light axis O and illuminates ahead of the lamp in a direction towards the light-emission via the inner lens 3. In this case, the above-described light is illuminated forwards so as to form a predetermined light distribution pattern along with a predetermined light distribution characteristic.
A second structure of a conventional vehicle lamp using an LED as a light source as shown in FIG. 9 is also well known. The structure is disclosed in, for example, patent document No. 3 (Japanese Patent Application Laid Open JP2007-123027). A vehicle lamp 4 shown in FIG. 9 is composed of an LED 2 located so as to emit light in a direction normal to an optical axis of the lamp 4 (an upward direction in FIG. 9) and a reflector 5 located over the LED 2. The LED is mounted on a circuit board 2a and the optical axis of the LED 2 is perpendicular to a light-emitting direction of the vehicle lamp 4.
The reflector 5 is configured with a reflector surface that forms an inner surface thereof and forms a concaved shape in a forward direction so as to reflect light emitted from the LED 2 forwards (a rightward direction in FIG. 9). More specifically, the reflector 5 is configured with a parabolic reflector such as a parabola revolving around the optical axis thereof extending in a direction towards the light-emission. A focus of the reflector is located near the light-emitting portion of the LED 2.
According to the vehicle lamp 4 of the above-described structure, the LED 2 is emitted and driven via a driving control by the driving circuit. Light emitted from the LED 2 passes upwards and is reflected by the reflector 5. Therefore, a substantially parallel light is illuminated forward in a direction towards the light-emission direction of the lamp.
Moreover, a third structure of a conventional vehicle lamp using an LED as a light source as shown in FIG. 10 is also well known. The structure is disclosed in, for example, patent document No. 4 (Japanese Patent Application Laid Open JP2005-183327) and patent document No. 5 (Japanese Patent Application Laid Open JP2007-087946). A vehicle lamp 6 shown in FIG. 10 is only composed of an LED 2 mounted on a substrate 2a so that an optical axis of the LED 2 extends perpendicular to the substrate 2a. In this case, a casing 7 shields sideward directed light emitted from the LED 2 so as not to cause glare.
According to the vehicle lamp 6 of the above-described structure, the LED 2 is emitted and driven by a driving circuit. Light emitted from the LED 2 is directly illuminated forward in a direction towards a light-emission of the vehicle lamp 6. In this case, the vehicle lamp 6 is configured so as to confirm to a predetermined light distribution standard in accordance with traffic laws using the directional characteristics of the LED 2. However, when an outer lens is located in front of the LED 2, the vehicle lamp 6 forms a light distribution pattern in accordance with characteristics of both the LED 2 and the outer lens.
The above-referenced Patent Documents are listed below.    1. Patent document No. 1: Japanese Patent Application Laid Open JP2005-276805    2. Patent document No. 2: Japanese Patent Application Laid Open JP2004-140090    3. Patent document No. 3: Japanese Patent Application Laid Open JP2007-123027    4. Patent document No. 4: Japanese Patent Application Laid Open JP2005-183327    5. Patent document No. 5: Japanese Patent Application Laid Open JP2007-087946
When a vehicle lamp using the above-described structures is devised, some problems, characteristics, and limitations may be caused. For example, when the first exemplary structure shown in FIG. 8 is used for a tail lamp, the tail lamp is required to maintain an illumination intensity that can be seen up to three hundred meters away according to Japanese traffic law. Therefore, the vehicle lamp 1 is required to control light emitted from the LED 2 using the lens formation 3a of the lens 3 so as to conform to a light distribution standard.
The vehicle lamp 1 may conform to a light distribution standard using a plurality of LEDs, etc. However, when the vehicle lamp 1 is observed from out of an area of a light distribution pattern formed in accordance with a light distribution standard, the vehicle lamp 1 may have low visibility because of a relatively small amount of light-emission from the LED 2, for instance, in a side view of the vehicle. In addition, because the vehicle lamp 1 includes the lens formation 3a in order to conform to a light distribution standard, the vehicle lamp 1 may not be good-looking and may have a pathetic outside appearance and an obsolete design.
In case of the above-described second structure shown in FIG. 9, the vehicle lamp 4 controls light emitted from the LED 2 using the reflex shape of the reflector 5 so as to conform to a light distribution standard. The vehicle lamp 4 may also conform to a light distribution standard using a plurality of LEDs, etc. However, when the vehicle lamp 4 is observed from out of an area of the light distribution pattern formed in accordance with light distribution standards, the vehicle lamp 4 may also have low visibility because of the relatively small amount of light-emission from the LED 2, for instance, in a side view of the vehicle.
When the third exemplary structure shown in FIG. 10 is in, for instance, a headlight, the headlight is required to illuminate up to one hundred meters away at a high beam distribution thereof according to Japanese traffic law. Therefore, the vehicle lamp 6 is required to control light emitted from the LED 2 so as to conform to this and other light distribution standards. However, it may be hard to select the LED 2 such that it has a large amount of light-emission and conforms to light distribution standards and also maintains a predetermined individual brightness in a predetermined light distribution pattern. The above-described problems and characteristics may be present not only in the LED 2 light source but also in other light-emitting semiconductor devices.
The disclosed subject matter has been devised to consider the above and other problems, features, and characteristics. Thus, an embodiment of the disclosed subject matter can include a vehicle lamp using a light-emitting semiconductor device as a light source with a favorable light distribution pattern and a vehicle lamp using a light-emitting semiconductor device as a light source with a simple structure and a high visibility, even if a person recognizing the vehicle is outside of an area of a light distribution standard and a driver of the vehicle sees a position beyond an area of a light distribution standard. In addition, the structure for the vehicle lamp in accordance with principles of the disclosed subject matter allows the vehicle lamp to form various futuristic novel and appealing outside appearances and design.